AD and diabetes are currently common and frequently-occurring diseases which seriously endanger the health of human beings. Particularly, their incidence is increasing with the growth of the population of the old. So the prophylaxis and treatment of these diseases become more and more critical.
Current preventive and curative drugs for AD are unlikely to revolutionize the treatment of AD due to their limitation of the mere symptomatic relief or severe adverse effects. The drugs commonly used for diabetes are mainly insulin and other orally hypoglycemic drugs, most of which are disadvantageous in inconveniency for use and toxicity. Particularly, there are actually no effective drugs for type 2 diabetes. It has been found that the occurrence of AD and type 2 diabetes is related to the deposition of amyloid-beta (Aβ) and amylin (IAAP) the subsequently fibrillogenesis and increased free oxidative radicals, which gives rise to the fact that inhibition of the fibril formation of amyloid-beta and amylin becomes the perspective for the prophylaxis and treatment of these diseases.
Alginates are the main components of cell wall of brown algae, which are linear anion polysaccharides composed of β-D-mannuronic acid (ManA) and α-L-guluronic acid (GulA), linked by 1-4 glucosidic bonds. Alginate belongs to high polymers with a molecular weight of several 104 to 106 with abundant sources. Alginate has been widely applied in food production, chemical engineering and medicine, etc. Recent study has revealed that alginate has a variety of bioactivities. However, its application as a drug is limited to a certain extent by its large molecular weight. Therefore, the oligosaccharide degraded from alginate by different methods is highly valuable for glycochemistry, glycobiology, glycoengineering and study of saccharide-based drugs, etc. The methods for degrading alginate include enzymatic, physical and chemical degradation, yet the requirement of specific enzymes has limited the application of enzymatic degradation. Physical degradation, which is usually used in combination with other methods, cannot easily provide oligosaccharides due to the ultimate molecular weight of about 50,000 Da of the products thereof. Chemical degradation used for polysaccharides include acidic hydrolysis and oxidative degradation. Acidic hydrolysis is limited by its capacity to get oligosaccharides with a molecular weight of 4000 or less when conducted at a normal temperature and under a normal pressure.